In the manufacture of transit vehicles, such as buses and rail cars, a recent and growing practice is to make the vehicle side walls, or at least portions thereof, of panels assembled from aluminum strakes extruded to exact dimensions. Embodied in these side walls may be various snap-on elements, which are applied after portions of the vehicle have been assembled, for example, extruded strips to cover the intersections of the side walls and roof or floor, or a plate or strip to cover an access area after the manufacturing procedures requiring access thereto have been completed. The prior art abounds with various types of snap-on fasteners, for example, as shown in U.S. Pat. Nos. 1,487,855, 3,120,971, 3,339,329, 3,508,369, 3,667,177, 3,732,659, and 3,760,544. While some of these prior patents may be usable to some extent for the purpose of the present invention, the latter has important structural and other features and advantages which distinguish if from any and all known prior art.